Normal hearing is binaural and provides significant advantages over monaural listening. Listeners with two ears are able to more accurately localize sound sources and more accurately understand a talker in the presence of spatially-separated, competing sound-sources. These advantages are a primary motivation for bilateral cochlear implantation. In this application, experts in cochlear implants and binaural hearing join in an effort to better understand the factors associated with today's bilateral sound-processing strategies that limit performance and to design, implement and test new sound-processing strategies that minimize those limitations. Five bilaterally-implanted subjects will be studied in depth using psychophysical studies to characterize their basic bilateral sensitivity to interaural time difference (ITD) and interaural level difference (ILD) using single and multiple interaural-electrode pairs. These sensitivities will be compared to those of three new methods of bilateral stimulation. To the extent these new methods improve the interaural sensitivity as measured at the level of interaural-electrode pairs, we propose to incorporate them in speechprocessing strategies to determine whether they improve functional performance in acute testing. Because today's sound-processing strategies limit a subject's access to the interaural sensitivity available at the individual electrodes, we also propose to implement and acutely evaluate two speech-processing strategies designed to overcome these limitations. Those speech-processing strategies that show promise in functional testing will be implemented for longitudinal testing to assess asymptotic performance and learning.